1. Field of the Invention
The present invention generally relates to an engine control apparatus for controlling the fuel injection, the ignition timing, etc., by using a microcomputer in an engine of a car, and particularly to an engine control apparatus for increasing a calculating speed so as to cope with- a high-speed revolution of an engine.
2. Description of the Prior Art
In the field of car engine, a method of electronically accurately controlling the quantity of fuel injection and the ignition timing of an engine by employing a microcomputer has been widely used in order to purify an exhaust gas, reduces fuel expenses and improve operating performance. FIG. 4 is a block diagram showing the arrangement of a practical example for executing such a conventional engine control method described above and for explaining the operation of the same.
In FIG. 4, there are provided various sensors 1-6 for detecting operation conditions of an engine (not shown), that is, a rotation sensor 1, a cylinder discrimination sensor 2, an air-flow sensor 3, a water temperature sensor 4, an idle switch 5, and an air-conditioner switch 6. The rotation sensor 1 is arranged to generate a pulse signal at a predetermined crank angle of the engine.
The cylinder discrimination sensor 2 is arranged to detect a predetermined rotational angle of a cam shaft of the engine. The air-flow sensor 3 is arranged to detect the quantity of suction air of the engine, and represented, for example, by air-flow sensor of a Karman vortex type, and of a hot-wire type.
The water temperature sensor 4 is arranged to detect a temperature of the engine. The idle switch 5 is arranged to operate when a driver's foot is removed from an accelerator pedal, and the air-conditioner switch 6 is arranged to represent an operating condition of an air conditioner provided in a vehicle.
The respective output signals of the rotation sensor 1, the cylinder discrimination sensor 2, the airflow sensor 3, the water temperature sensor 4, the idle switch 5, and the air-conditioner switch 6 are applied to a microcomputer 8 through an input circuit 7. The input circuit 7 is arranged to perform level conversion and filtering of the respective output signals of those sensors.
The microcomputer 8 is arranged to calculate the quantity of fuel injection, the ignition timing, and the quantity of control of an idle rotational speed control (ISC) actuator 12 on the basis of the foregoing input signals. FIG. 5 shows the internal arrangement of the microcomputer 8.
In FIG. 5, the microcomputer 8 is provided with a microprocessor 82 for taking-in various input signals through an input port 81 so as to execute calculation on the basis of a calculation procedure stored in an ROM (read only memory) 83 in advance, an RAM (random access memory) 84 for temporarily storing data obtained by calculation and a timer 85 for measuring a pulse period of the rotation sensor 1 and for generating a driving pulse width for injectors 10a-10d of FIG. 4.
The results of calculation of the micro-processor 82 are sent to an output port 86. Pulse signals sent through the output port 86 are amplified by an output circuit 9 in FIG. 4 so as to control the driving period and driving pulse width for the injectors 10a-10d and so as to control the on/off timing for ignition coils 11a and 11d.
In this example, four injectors are respectively correspondingly provided for four suction air pipes of a 4-cylinder engine so as to be driven separately from each other, and one ignition coil is provided for each pair of the four cylinders in which the compression and exhaust strokes are produced in phase, so that each pair of the four cylinders are ignited simultaneously.
In addition to the foregoing control of the quantity of fuel injection and the ignition timing which is the fundamental engine control, the driving pulses for the ISC actuator 12 for controlling the quantity of suction air of the engine in accordance with a water temperature and various load conditions and for a solenoid valve 13 for controlling the quantity of exhaust gas re-circulation (EGR) are controlled by the microcomputer 8 in the same manner as the case of the foregoing control.
In the thus arranged engine control apparatus, operation is executed in accordance with the flowchart of FIG. 6. In FIG. 6, a pulse N.sub.e generated by the rotation sensor 1 and a pulse N.sub.c (a cylinder discrimination signal of the diagram (b) of FIG. 7) generated by the cylinder discrimination signal 2 are read-in in a step S10, and a signal Q.sub.a of the air-flow sensor 3 is read-in in a step S11. A period of the pulse of the rotation sensor 1 is measured so as to obtain the engine speed N, and the quantity of fuel required per stroke, that is, a fundamental fuel injection pulse width .tau..sub.0 (=Q.sub.a /N), is calculated in a step S12.
Signals, for example, an output signal of the water temperature sensor 4 representing a temperature of the engine, an output signal of an oxygen sensor (not shown) for detecting an exhaust gas component, an output signal of an atmospheric pressure sensor (not shown), and the like, which moderately change, are readin in a step S13.
The quantities of correction (C.sub.1, C.sub.2,...) stored in the ROM 83 in advance are read out correspondingly to those correction input signals, and the total correction coefficient C=C.sub.1 .times.C.sub.z .times.... is obtained by an operation of interpolation in the step S14.
The fundamental fuel injection pulse width .tau. which has been already calculated is multiplied by the correction coefficient C to thereby determine a pulse width for actually driving the injectors 10a-10d in a step S15.
As shown in FIG. 7, the injectors 10a-10d are driven by the pulse width .tau. (the diagram (C) of FIG. 7) by using the rotation of the engine, that is, the output signal (the diagram (a) of FIG. 7) of the rotation sensor 1 as a reference of triggering.
Among various values of the ignition timing .theta. stored in advance in the form of a map in the ROM 83 with respect to various values of two parameters, the engine speed N and the engine load condition (Q.sub.a /N), a proper value is read out so as to obtain a fundamental ignition timing .theta..sub.0 through operation of interpolation in a step S16.
The quantity of ignition timing correction .theta..sub.c is calculated correspondingly to the engine temperature and existence of an idle state of engine in a step S17, and an actual ignition timing, that is, a timing for cutting-off a current flowing in the ignition coil 11a/11b, is obtained in a step S18.
An initiation timing .theta..sub.d of current-conduction of the ignition coil 11a/11b is controlled so that a period of time (.theta.-.theta..sub.d) is always substantially constant, that is, the ignition coil 11a/11b is controlled so as to make .theta..sub.d (a phase angle) shorter as the engine speed becomes higher.
After the control of the fuel injection and the ignition timing has been executed in the foregoing steps S10-S18, the quantity of control of the ISC actuator is calculated on the basis of the on/off state of the air-conditioner load and the engine temperature in a step S19. Further, if necessary, variable valves for an EGR system and a suction air system are controlled in a step S20.
In the conventional engine control apparatus, as described above, all the operations required for the control of the fuel injection pulse width, the on/off-control of the ignition coil (the diagrams (f) and (g) in FIG. 7), the control of the ISC actuator, and the like, have been executed by a single microcomputer 8.
As shown in FIG. 7, generally, the operation by a microcomputer is carried out such that the injection pulse width (the diagram (c) of FIG. 7) is calculated in a period of time t.sub.1 by using the rotational signal (the diagram (a) of FIG. 7) as a trigger signal and the injector driving pulse width .tau.(the diagram (d) of FIG. 7) is determined on the basis of results of the above calculation.
Next, the ignition timing is calculated in a period of time t.sub.2 as shown in the diagram (e) of FIG. 7, and results of calculation are used as the actual ignition timing on the basis of the succeeding rotational signal.
Further, the calculation for the idle rotational speed control and EGR control is carried out in a period of time t.sub.3 (the diagram (h) of FIG. 7). The sum of the time t.sub.1, t.sub.2, and t.sub.3 required for the calculation reaches several msec., and in a 4-cylinder engine, calculation time reaches a value approximate to a limit because the p[period (t.sub.0)] of the rotational signal is 5 msec. at 6000 rpm. Therefore, it has been difficult that the conventional control apparatus copes with a high engine speed of 7000-9000 rpm.